The present invention relates to a magnetic brush apparatus and, more particularly, to a magnetic brush apparatus for developing an electrostatic latent image on a photosensitive body or cleaning the photosensitive body in an electrophotographic apparatus.
Generally, in a electrophotographic copying machine, a developing apparatus with a magnetic brush is used to develop an electrostatic latent image formed on the surface of a photosensitive body. The magnetic brush contacts the photosensitive body to electrostatically transfer the positively or negatively charged developer onto the surface of the photosensitive body.
In a copying machine of this type, after the developing step as described above, the developer on the surface of the photosensitive body is transferred onto a paper sheet. A cleaning apparatus is used to remove the residual toner remaining untransferred on the surface of the photosensitive body.
A developing apparatus and a cleaning apparatus as shown in FIGS. 1 and 2, respectively, are conventionally known.
As shown in FIG. 1, in a conventional developing apparatus 2, magnetic poles 6 arranged at one side of a magnet roller 4 are set at positions to oppose a photosensitive layer 8 of a photosensitive drum. When a sleeve 10 rotates in a direction indicated by arrow M, developer 14 in the form of a brush is taken out of a casing 12 and is brought into contact with the photosensitive layer 8. The developer 14 which does not attach to the photosensitive layer 8 but remains on the sleeve 10 is returned into the casing 12 as the sleeve 10 further rotates. A fixed scraper 17 constantly contacts the surface of the sleeve 10 so as to scrape off the residual toner 14 on the sleeve 10. After developing, the magnet roller 4 is rotated through about 180.degree. in the direction indicated by arrow M, so that the magnetic poles 6 are positioned away from an opening in the casing 12 and the rotation of the sleeve 10 is interrupted.
When the developing operation is resumed, the magnet roller 4 and the sleeve 10 are rotated in the direction indicated by arrow N, and the developer is brought in the direction from the scraper 17. However, since the scraper 17 constantly contacts the sleeve 10, the developer is scraped off. For this reason, when the rotating of sleeve 10 starts a magnetic brush of a suitable contour is not formed, so that a sufficient amount of developer is not attached to the photosensitive body 8, resulting in defective developing.
Meanwhile, in a conventional cleaning apparatus 18 shown in FIG. 2, a plurality (four in this case) of scrapers 22, 24, 26 and 28 which may be brought into direct contact with or separated from a photosensitive layer 20 of a photosensitive body are arranged so as to separately recover residual developers of respective colors from the photosensitive layer 20. These scrapers are brought into contact with the photosensitive body to clean it. However, in this conventional cleaning apparatus, since the scrapers directly contact the photosensitive layer 20, the relatively expensive photosensitive layer 20 may be abraded or damaged or formed a film of developer by rubbing of scraper. Thus the service life of the photosensitive layer is shortened.